// 1像素边框
border-1px($color)
  position: relative
  &:after
    display: block
    position: absolute
    left: 0
    bottom: 0
    width: 100%
    border-top: 1px solid $color
    content: ' '
// 消除1像素边框
border-none()
   &:after
     display none  
// 根据分辨率自己传入图片
bg-image($url)
  background-image: url($url + "@2x.png")
  @media (-webkit-min-device-pixel-ratio: 3),(-min-device-pixel-ratio: 3)
    background-image: url($url + "@3x.png")